Spark plug and method of making the same



Aug; 6 9 'H. RABEZZANA. 1,872 496 SPARK PLUG AND METHOD OF MAKING THE SAME Filed Dec. 7, 1928 Patented Aug. 16, 1932 UNITED STATES- PATENT OFFICE HECTOR RABEZZANA, OF FLINT, MICHIGAN, ASSIGNOR TO A C SPARK PLUG COMPANY, OF FLINT, MICHIGAN, A COMPANY OF MICHIGAN SPARK PLUG AND METHOD OF MAKING THE SAME Application filed December 7, 1928. Serial No 324,512.

This invention relates to spark plugs for internal combustion engines, and more particularly to mica-insulated spark plugs in which annular constrictions and/or deformations of an outer metallic shell are employed to hold previously-compacted washers of mica or the like under radial comshouldered washer, (3) an inner electrode,-

optionally tapered, and means such as (4:) a collapsed nut to retain exterior insulation. Although affording large insulation surface, this construction is such that heat and pressure, as generated by the explosions in the engine, can have little or no detrimental effect even when these plugs are used in high corppression, high speed, hot running engines toward which there seems to be a present trend.

It is another object of this invention, utilizing a discovery that radial compression may be satisfactorily transm tted through mica washers after they have been placed under high axial compression, to provide a spark plug in which such washers or the like are compressed by deformation of corresponding surfaces of shells servingas parts ofplug bodies; and said bodies may initially comprise a zone or zones adapted to be thermoplastically collapsed, as by a local heating under a pressure which compels said washers so closely to fit the other plug parts as substantially to prevent gas leakage.

It is a further object of this invention, in which a radial compression may be effected by the use of inwardly-diminishing electrode heads or stems,to provide novel and improvedv methods of making spark plugs,methods which facilitate accuracy, economy and speed in production, and low cost, and which provide exceptionally reliable and durable spark plugs, so designed as substantially to exclude water.

These methods preferably involve both a wedge fit and a local and suitably timed use of electrical resistance heating of the parts under pressure; but other objects of this inven: tion (all forms of which may involve some use of a washer-receiving receptacular shell which initially includes an lip-standing flange and/or a mentioned collapsible zone. an inwardly-diminishing electrode head being optionally wedged therein after a taperreaming operation, when such is included) will become apparent upon reference to the appended, claims and the accompanying drawing, wherein Figure 1 is an elevation, partly in section, of a spark plug made in accordance with the present invention;

Figures 2,3, 4 and 5 are sectional views, and Figure 6 an elevation, partly in section, illustrating various steps in the method of assembling the plug parts;

Figure 7 is a sectional view of a ortion of a spark plug illustrating a modi cation;

Figure 8 shows a further modification.

Referring to the drawing, the reference character 1 indicates the outer metal shell, having a screw threaded portion 2 at its lower end, an upwardly extendin flange or lip 3 at its upper end, and a wea ened wall portion 4 at an intermediate point. Positioned within the bore of the shell are several layers or washers of insulating mate-' rial, such as mlca, arranged in two groups 5- form or bulge, thereby shortenin annular flange 8 and over which the up-standing lip 3 is swaged or bent upon the application of pressure, as is illustrated in Figure 3. In this figure there are shown die members 9 and 10, which are moved together against opposite ends of the shell 1, bending or guiding the lip 3 against the disc 7, thereby exerting a clamping pressure upon the laminated bodies and moving'the several layers closer together,-and locking the parts against subsequent separation. As soon as the parts are locked by the die members 9 and 10, the weakened wall 4 is preferably subjected to heat; further application of pressure by the die members 9 and 10 causes this wall to de- 0 the length of the shell and serving to radially compress the laminated insulation. The subsequent contraction of the metal upon cooling serves to still further exert a clamping pressure upon the layers of mica and upon a central electrode, if present. Otherwise, the top surface of the in-turned lip 3 may be machined or dressed down flat; and a reaming tool, such as indicated by the numeral 11, may be inserted in the central bore from the bottom to make the lower end of the bore tapered or cone shaped. A central electrode 12 having a tapered head or conical lower end 13 for seating engagement with the tapered surface of the insulation may be extended through the central bore to a point considerably above the top of the shell. An insulating sleeve 14 may be placed over the stem of the electrodeand fitted through the central opening in the washer '7 and the opening in the insulator body 6. Laminated bodies 15 and 16 are shown placed on the stem 12 above the top of the shell 1, as is also a retainer or nut 17, having an annular groove therein to provide aweakened wall 18. The parts may be then inserted in the dies.9,10 or dies 19 and 20, the die member 20 havinga relatively movable stem 21 7 extending therethrough, said stem being shown as carried by pressure limiting means and as having a socket tip 23 for engagement with the lower end of the electrode to .press it until secured in fitting engagement with the conical surface rovided by the tapered bore in the body 5. (glamping pressure exerted b the die members mentioned compresses the aminated groups 15 and 16, and then causes the collapse of retainer member 17. The weakened wall 18 is preferably heated so that upon its collapse the material that is moved into tight contact with the screwthreaded end of the electrode will weld or fuse with the material of the electrode, there by forming a permanent connection and one that serves both to hold the parts in assembly and the upper insulating body, comprising the laminated groups 15 and 16, under compression. The close fit between the several parts and the compression of the lami.

nated disc serves to effectually seal the plug against leakage of gas from the combustion chamber, head 13 preferably extending opposite bead 13'.

The insertion of the'electrode 24 in the lower end of the shell in spaced relation with the electrode 12 to provide a spark gap, and the dressing down of the upper portion of the shell along the dot-and-dash lines shown in Figure 6 to afford a finished appearance to the plug, complete the several steps in the manufacture of the plug involved in the present-invention, in some forms thereof.

In Figure 7 the central electrode 25 is surrounded by a long insulator sleeve 26 extending through the main insulation 27. Electrode 12 or 25 may be provided in its lower end with a fiat head 28 fitting against a shoulder formed in the insulating bod '27. The deformation of the weakened wal 29 of the shell 30, as previously described, exerts an inward force upon the insulation or upon a protective sleeve 31, tendin to crowd the adjacent laminae radially. his causes the sleeve 26 to tightly hug or grip the sides of the head 13 or electrode 25, thereby providing an effective seal against gas leakage. The structure of the plug is otherwise as before described. The sleeve 14 or 26, if used, may be formed of mica; the sleeve 31 may be of comparatively thin and ductile metal; and any or all of the mentioned deformations may advantageously be effected in an electric welding machine comprising the mentioned dies,somewhat as suggested by the use of plus and minus signs in Fi ures 3,.6 and 7; but the axial effect obtaine by any application of heat and pressure to the deformable zone 4 may be observable mainly on a cooling thereof.

It will be obvious that dies 10 and 20 may be identical and stationary; that dies 9 and 19, then movable, may not be identical; and that die 21 (preferable, in point of convenience, to such means as might alternatively be employed to advance or place the stem 12 or 25 under tension before one or more retaining elements are locked thereon) may be supported by resilient means somewhat as symbolized by a compression spring 32, adapted to yield under a predetermined pressure.

In order to avoid separation or distortion of, or ,other harm to, the mica washers or equivalent insulation, any thermo-plastic or other inward collapse of the weakened region 4 or 29 of the receptacular shell 1 or 30, to effect a radial compression, obviously should occur, if at all, subsequent to any thermo-plastic or other inward deformation of the lockin flange 3; and the die 9 and the flanges 3 an 8, or equivalent parts, may, in fact, be so proportioned and used as not only to effect and maintain a desired longitudinal or axial compression (and even to surfaces) obviate an machining of the die-contacted ut to produce, in the sequence indicated, the' desired radial compressive efl'ect,obviatin leakage past any suitable insulation assem 1y within a shell.

It will be seen that all the described forms of present invention contemplate some use of sheaves of non-vitreous and substantially non-fracturable insulation snugly fitting a special shell which is receptacular in form, this being provided with an inner insulationreceiving cylindrical or other corresponding surface which downwardly terminates in a flat or approximately flat washer-receiving surface (to seat a sheaf 5 or 28 of washers, spacing an inner terminal portion of an electrode head) and upwardly terminates in a restraining part such as deformable flange 3; that any protective sleeve 31 employed to effect a favorable distribution of pressure upon insulation (and Whether integral with or distinct from the washer 7) ma well be slightly shorter than the sheaf 27 o insulating washers to be thereby protected; and that those embodiments suggested in Figures 7 and 8 obviously presuppose the use of some electrode-positioning means (which,

may be such as are suggested in Figure 6) during the placing of some of the washers of any inner electrode assembly (as typified by sheaves 5, 5f and/or sheaves 27, 28 and 28 under radial compression,the reaming operation suggested in Figure 4 being ordinarily used, to provide a tapered electrode seat,=only in case a wedge-fitting or other inwardly-diminishing electrode is to be inserted subsequently to a radial compression, to be retained under'tension by means suchas a welded-on or other nut 18.

As suggested above and in Figure 8, re-

gardless of whether or not means such as insulation-protecting tubes 31, 31 are employed opposite regions of deformation and for a pressure-distributing or cleavage-preventing or other effect, and regardless of whether any members comparable to the flange 8 are provided (as by tubes 8, shown as separate from washers 7 and as adapted to receive mica or otherinsulating sleeves 26) any regions or parts opposite the flanges or beads resulting from deformation, and thereby subjected to radial pressure, may be protected by yieldable metallic or other tubes of suit-able length; and it is suggested in Figure 8 that an alternative or additional and intermediate sealing and retaining effect may be obtained by so proportioning the flange 3 and the tube 8, and so shaping the die 9' and retaining element 7' that, in addition to or instead of any inward collapse of a weakened region 4 or 29, a suitable deformation of such a flange shall incidentally produce a sealing and electrode-gripping joint by an inward compression 'of insulating sleeve 26 ,-whether or not a protecting tube 8' is inter osed in addition'to or in preference to any ange on the shouldered retaining washer element 7 and whether or not an suitably timed electrical or other heating is concurrently employed; but the suggested protection and a brief use of a softening electrical heat are both considered advantageous,- the electrical heating being favored by the 10- cal resistance due to a reduction in cross sectional area in the deformable region or regions. G v

' In that simple and very practical embodiment shown Figures 1 and 5, only the tapered head 13 and a so-called nut 18 need be employed as stop elements to retain under compression an outer (and at least part ofan inner) insulation assembly assumed to be formed of mica or of a like non-vitreous material; but the concurrent use of axial compression and radial pressure, as rovided for by the delayed constriction e ected at 4 (preferably opposite the taper of the head 13) is found to assure permanent tightness even in the case of thls very inexpensive form,both the effects of opposite or radially compressive movements of surfaces in assembling as described and the effects of enormous gas pressure which result from explosures during use being favorable to a. tight gripping of an electrode stem and/or a tight seating of the conical or other inwardly-diminishing head 13; and it will be ap reciated that, although the collapsed or de ,ormed receptacular shell might serve alternately as a bushing within a threaded body carrying a grounded electrode, the incidental compression of an auxiliary sheaf of head spacing washers or the like, as at 5' and 28', is an' important merit of the described construction and method.

Although the foregoing descri tion suggests but a limited number of em odimentsr and advantages of this invention, it should be understood not only that various features thereof might be independently employed,

but also that numerous additional modifications thereof might easily be devised,'-all without involving the slightest departure from said invention, as the scope thereof is indicated above and in the following claims.

I claim:

as to place said insulation first under axial and then under radial compression, said insulation comprising mica washers and an electrode being so inserted as to effect a gastight joint with some of said washers.

3. A method of securing an inner electrode in gas-tight relationship to mica washers surrounded by a metallic shell which comprises applying opposite pressures to the electrode and a retaining element therefor, and thermoplastically collapsing the retaining element.

4. A method of securing an inner electrode in gas-tight relationship to mica washers surrounded by a metallic shell which comprises applying opposite pressures to the electrode and a retaining element therefor, and thermoplastically collapsing the retaining element, said washers being taper-reamed while under compression, and said electrode being provided with an head.

5. A method of producing a spark plug which comprises: disposing mica washers within a shell element having a corresponding inner surface, inserting an electrode element having an inwardly-diminishing surface; and producing such relative movement of one of said surfaces, while holding said washers compacted, as to effect a radial compression of some of said washers and to produce substantially gas-tight joints adjacent thereto.

6. A method of producing a tight joint between an outer shell element and an insulation assembly therein which is characterized by thermoplastically eifectin an inward collapse of said shell while hol ing said assembly under axial compression.

7. In a method of making spark plugs that comprise axially-compacted non-vitreous insulation elements: compacting said insulathermoplastically so deforming said shell as permanently to retain said insulation elements under the desired compression.

8. A method of providing spark plugs with mica washers insulation held under ra dial compression between concentric conductive elements which includes manipulating one of said conductive elements to compress the insulation in a manner that such compression is radially transmitted, through said washers, to the other of said conductive elements.

9. A spark plug comprising: a receptacular metallic shell having non-vitreous flat washer insulation elements held under edgewise compression therein by a collapsed part of said shell.

10. A spark plug comprising: a receptacular metallic shell having non-vitreous flat washer insulation elements held under radial compression therein by a collapsed part of said shell,said part comprisingan inwardly inwardly-diminishing extending annular region, radially compressing some of said insulation elements.

11. A'spark plug comprising: a receptaculaf metallic shell having non-vitreous insulation elements held under compression therein by a collapsed part of said shell,said part comprising an inwardly extending annular region, radially compressing some of said insulation elements, and an insulation-protecting tube being disposed opposite said region.

12. A spark plug comprising: a receptacular metallic shell having non-vitreous insulation elements held under compression therein by deformed portions of said shell,-said portions involving an inwardly bent flange, for axial compression, and an inwardly extending head, for radial compression of some of said insulation elements.

13. A spark plug comprising: non-vitreous insulation elements compressed within a shell and collectively providing a tapered electrode seat; and an inwardly-diminishing electrode retained under tension within said seat,said shell being inwardly deformed and an insulating sleeve being disposed on said electrode opposite a region of inward deformation of said shell.

14. spark plug comprising: non-vitreous insulation elements compressed within a shell and collectively providing a tapered electrode seat; and an inwardly-diminishingelectrode retained under tension within said seat,--said electrode externally carrying an insulation assembly which is retained under compression by awelded-on nut, said electrode comprising a wedge-fitting portion and said shell being provided with an inwardly-extending bead opposite the wedge-fitting portion of. said electrode.

15. In aspark plug: an assembly of insulating washers; a conductive shell element snugly fitting the edges of the washers and retaining some of said washers'under axial compression; an inner and tensionable conductive element extending through some of said washers; and a deformed portion associated with one of said' conductive elements, for placing and retaining some of said washers under radial compression.

16. In a spark plug: an assembly of insulating washers; a conductive shell element snugly seating and retaining some of said washers under axial compression; an inner and tensionable conductive element extending through some of said washers; and means, comprised in one of said conductive elements, forplacing and retaining some of said washers under radial compression, said shell comprising a region of inward deformation and a portion of said tensionable element opposite the region of inward deformation and a portion of said tensionable element opposite the region of inward de formation of said shell being surrounded by an insulating sleeve.

17. For use in a, spark plug comprising an asesmbly of insulating washers: a receptacular shell element interiorly providing, near one end thereof, a seat for the direct reception and support of such washers,-said shell element being provided also with an inwardly deformable flange, at its opposite end, and with an inwardly and subsequently deformable intermediate zone having relatively high electrical resistance.

In testimony whereof I aflix my signature.

HECTOR RABEZZANA. 

